1. Field of the Invention
The present invention relates to a wiring circuit board having bumps, where the bumps are of a uniform height, and a method of manufacturing the same.
2. Description of the Related Art
Microscopic bumps (for example, bumps being a diameter of 50 μm and a height of 30 μm) are widely used when connecting electronic components such as a semiconductor device and a liquid crystal display device to a wiring circuit board, or when connecting the layers of a multi-layer wiring board.
A typical method of forming bumps of this size is shown in FIGS. 5A to 5E.
Specifically, first, as shown in FIG. 5A, a 2 layer flexible board 53 is made up of a polyimide film 51 on a copper foil 52, and copper foil 52 is patterned by photolithography to form a wiring circuit 54 (FIG. 5B).
Next, a cover coat layer 55 is formed on wiring circuit 54 in accordance with conventional methods (FIG. 5C). For example, cover coat layer 55 can be formed by forming a polyamic acid layer on wiring circuit 54, patterning by photolithography, and imidization. Alternatively, a resist ink may also be printed thereon.
Next, the area on polyimide film 51 that corresponds to wiring circuit 54 is irradiated with laser light to form bump holes 56 (FIG. 5D). Then, after covering cover coat layer 55 with a protective film as needed (not shown in the Figures), microscopic bumps are formed by growing metal bumps 57 by means of electrolytic plating on the portions of wiring circuit 54 that are exposed in the bottom of bump holes 56 (FIG. 5E).
However, when opening bump holes 56 by means of laser irradiation, there is a problem with variations in open space due to variations in the amount of smear adhered to the bottom of bump holes 56, and as a result, there is a problem with large variations developing in the height of metal bumps 57. Because of this, stable bump connections are difficult. In particular, connecting semiconductor devices to the wiring circuit in one batch by means of ultrasound is difficult. In addition, a plating pre-treatment is essential in order to improve the strength of the adherence between wiring circuit 54 and the metal bumps 57 formed thereon.